1. Field of the Invention
The present invention relates to a rear projection screen including a Fresnel lens sheet. More particularly, the present invention relates to a rear projection screen capable of displaying sharp images without producing ghost or double images, and to a rear projection type display including such a rear projection screen.
2. Description of Related Art
So-called rear projection type displays, which include rear projection screens on which light (imaging light) is projected from their back sides, are known as displays having large-sized screens.
As shown in FIG. 3, a conventional rear projection type display 101 is composed of: a rear projection screen 103; a projector 105 for projecting light 106 on the rear projection screen 103; and a reflector 104 for reflecting the projected light 106 into the back-side surface of the rear projection screen 103. The rear projection screen 103, the projector 105 and the reflector 104, which are positioned as shown in FIG. 3, are contained within a cabinet 102. Namely, the rear projection screen 103 is set in a bored window made in the upper part of the front (observation-side) surface of the cabinet 102, and the projector 105 is placed at the lower part in the cabinet 102. The reflector 104 is placed at the upper part in the cabinet 102 so that it can reflect the light 106 projected from the projector 105, into the back-side surface of the rear projection screen 103.
FIG. 4 is a view showing a typical rear projection screen 103 for use in the rear projection type display 101 shown in FIG. 3. As shown in this drawing, the typical rear projection screen 103 includes a Fresnel lens sheet 111 on its back side and a lenticular lens sheet 121 on its observation side. The Fresnel lens sheet 111 and the lenticular lens sheet 121 are positioned in close proximity in the rear projection screen 103; in general, they are closely fitted. The Fresnel lens sheet 111 has a Fresnel lens 112 on its observation-side surface and a flat surface 114 as its back-side surface. The lenticular lens sheet 121 has lenticular lenses 122 on its back-side surface (the surface facing to the Fresnel lens sheet 111) arranged so that grooves will be vertically formed between the lenticular lenses. Further, on the observation-side surface of the lenticular lens sheet 121, black stripes 123 for preventing the reflection of light entering from the observation side of the lenticular lens sheet 121 are formed on those parts corresponding to the non-light-converging parts of the lenticular lenses 122 provided on the back-side surface of the lenticular lens sheet 121.
In the rear projection type display 101 having the above-described arrangements, when light 106 projected from the projector 105 is reflected from the reflector 104 into the back-side surface of the rear projection screen 103, most of the incident light passes through the rear projection screen 103 and becomes imaging light 107. However, the back-side surface of the rear projection screen 103 reflects a part of the incident light, and the reflector 104 reflects this reflected light 108 into the rear projection screen 103. The reflected light 108 thus re-enters into the rear projection screen 103 at the point different from the one at which the projected light 106 has firstly entered, and finally emerges as ghost light 109 from the observation side. For this reason, when the rear projection screen 103 in the rear projection type display 101 is observed, ghost images are seen in addition to the properly reflected image in a position deviated from that of the properly reflected image. Such ghost images tend to appear when the optical path length between the projector 105 and the rear projection screen 103 (i.e., projection distance) is shorter and when the distance between the rear projection screen 103 and the reflector 104 is shorter. The appearance of ghost images is therefore a big problem encountered in attempts to make the rear projection type display 101 thinner.
A conventionally proposed measure for preventing the appearance of ghost images is such that an antireflection layer is formed on the back-side surface of a rear projection screen. With this measure, however, it is difficult to perfectly prevent the appearance of ghost images although it is possible to make the intensity of ghost images lower. Moreover, it is necessary to conduct vacuum deposition or the like to form an antireflection layer on the back-side surface of a rear projection screen. This process is poor in production efficiency, so that the above-described measure is inadequate from an industrial point of view.
On the other hand, Japanese Laid-Open Patent Publication No. 158153/1993 discloses the following measure of preventing the appearance of ghost images: the back-side surface of a Fresnel lens sheet to be used for a rear projection screen is roughened by forming crepe finish, hair lines, lenticular lenses or the like; in particular, lenticular lenses are provided in such a direction that grooves will be horizontally formed between the lenticular lenses. However, if the back-side surface of a Fresnel lens sheet is simply roughened in the manner as disclosed in this publication, the projected image tends to have lowered definition and contrast. Moreover, the formation of lenticular lenses on the back-side surface of a Fresnel lens sheet promotes the appearance of a moire pattern.
The present invention was accomplished in the light of the foregoing drawbacks in the related art. Namely, an object of the present invention is to provide a rear projection screen that can effectively prevent the appearance of ghost images which is caused by projected light reflected from the back-side surface of the rear projection screen, that can be excellent in production efficiency, that can display an image having satisfactorily high definition and contrast, and that does not promote the appearance of moire patterns; and a rear projection type display including such a rear projection screen.
Another object of the present invention is to provide a rear projection screen that scarcely undergoes curling, which leads to the lowering of image definition, with changes in environmental conditions such as change in humidity; and a rear projection type display including such a rear projection screen.
The present invention provides a rear projection screen comprising a Fresnel lens sheet that converges projected light entering from a back side thereof and allows the converged light to emerge from an observation side thereof, wherein the Fresnel lens sheet has an observation-side surface forming a Fresnel lens and a back-side surface forming a matte surface.
In the present invention, the Fresnel lens sheet preferably has a haze value defined in JIS (Japanese Industrial Standards) K7105 of 15 to 40%. Further, the matte surface of the Fresnel lens sheet preferably has a 60xc2x0 specular gloss defined in JIS K 7105 of 20 to 45% and a 20xc2x0 specular gloss defined in JIS K7105 of 5 to 15%.
Further, in the present invention, it is preferable that the Fresnel lens sheet includes a cured material layer formed by curing an ionizing-radiation-curing resin and a transparent substrate sheet laminated to the cured material layer; the Fresnel lens is formed in the cured material layer; and at least a surface of the transparent substrate sheet not facing to the cured material layer is matted to give the matte surface.
Furthermore, in the present invention, the transparent substrate sheet in the Fresnel lens sheet preferably shows a water absorption of not more than 0.2% when determined by immersing it in water at 23xc2x0 C. for 24 hours under JIS K7209.
Furthermore, in the present invention, the Fresnel lens sheet preferably has a thickness between 0.2 mm and 1.5 mm.
Furthermore, in the present invention, it is preferable to subject the matte surface of the Fresnel lens sheet to antistatic treatment.
Moreover, it is preferable that the rear projection screen of the present invention further comprises a lenticular lens sheet on the observation side of the Fresnel lens sheet.
The present invention further provides a rear projection type display comprising: the above-described rear projection screen; a projector that projects light on the rear projection screen; and a reflector that reflects the projected light into the back-side surface of the rear projection screen.
According to the present invention, since the Fresnel lens sheet has a matte surface as its back-side surface, it is possible to effectively prevent the appearance of ghost images that is caused by projected light reflected from the back-side surface of the Fresnel lens sheet.
Further, according to the present invention, in the case where the haze value defined in JIS K7105 of the Fresnel lens sheet is made 15-40%, it becomes possible to effectively prevent the lowering of image definition and contrast.
Furthermore, according to the present invention, in the case where the 600 specular gloss defined in JIS K7105 of the matte surface of the Fresnel lens sheet is made 20-45%, the image contrast is not greatly lowered; in addition, the appearance of ghost images is more effectively prevented because such a matte surface can ensure the reflecting properties of light that is re-reflected from a reflector or the like and enters into the Fresnel lens sheet at a large angle.
Furthermore, according to the present invention, in the case where the 20xc2x0 specular gloss defined in JIS K7105 of the matte surface of the Fresnel lens sheet is made 5-15%, it becomes possible to restrain the reflection of light that enters into the Fresnel lens sheet almost vertically, so that the image contrast is not greatly lowered.
Furthermore, according to the present invention, in the case where the Fresnel lens sheet is made from a cured material layer formed by curing an ionizing-radiation-curing resin and a transparent substrate sheet to separately form a layer having a Fresnel lens and a layer having a matte surface, each layer can fully show its function; in addition, improvement in production efficiency can be attained.
Furthermore, according to the present invention, in the case where the water absorption of the transparent substrate sheet in the Fresnel lens sheet as determined by immersing the transparent substrate sheet in water at 23xc2x0 C. for 24 hours under JIS K7209 is made not more than 0.2%, the Fresnel lens sheet scarcely undergoes curling with changes in environmental conditions such as change in humidity, so that the lowering of image definition hardly occurs.
Moreover, according to the present invention, in the case where the thickness of the Fresnel lens sheet is made between 0.2 mm and 1.5 mm, it becomes possible to prevent the Fresnel lens sheet from curling and to effectively prevent the appearance of double images that is caused at the lower part of the Fresnel lens sheet.
In addition, according to the present invention, in the case where the matte surface of the Fresnel lens sheet is subjected to antistatic treatment, it becomes possible to improve both anti-dusting and anti-staining properties.